There are several pairs of athletes who will be competing for the United States at the London 2012 Olympic Games, but here are two sports in particular with duos to follow.

1.) Beach Volleyball: In this sport, Team USA has two of the most dominant pairs of athletes in the world with Misty May-Treanor and Kerri Walsh and Todd Rogers and Phil Dalhausser. May-Treanor and Walsh are the two-time defending Olympic champions, but a lot has happened since they last struck gold four years ago in Beijing. Walsh gave birth to her second child in 2010, and May-Treanor suffered an Achilles injury while practicing for the TV hit, “Dancing With The Stars.” But the duo has regrouped and is ranked third in the Olympic rankings entering London. Brazil’s Juliana Silva and Larissa França, who beat May-Treanor and Walsh in the gold-medal match at the world championships last year, is considered the team to beat. As for Rogers and Dalhausser, the gold medalists from Beijing, they are No. 2 in the Olympic rankings and have an uphill battle awaiting them in London. Dalhausser sprained his ankle last year at the FIVB World Tour Beijing Grand Slam and Dalhausser again was injured this past week at the FIVB World Tour Klagenfurt Grand Slam. Rogers and Dalhausser forfeited in the bronze-medal match but have said they will be OK for London.

2.) Synchronized Swimming: Mariya Koroleva and Mary Killman, better known as “MK Squared,” have not been together long, but they have made the most of their time together. Six weeks after becoming a duet team, they earned a silver medal at the Pan American Games. Now they are hoping to make their mark in the London 2012 Olympic Games. Just a month ago, Koroleva and Killman scrapped their free routine and created a new one, complete with Beethoven’s “Ode to Joy” and the Olympic theme song. The last time Team USA won the duet event at the Olympic Games was when when twin sisters Karen and Sarah Josephson did it in 1992. Koroleva and Killman are the lone synchronized swimmers representing Team USA in London; the United States did not qualify in the team event.

Double Vision

If you tune on the TV to catch some of the Olympic competition and think you are seeing double, do not run straight to the eye doctor. You might be seeing twins or siblings competing in the same sport.

1.) Twins: Team USA features two sets of twins on its 2012 Olympic Team: Bob and Mike Bryan in tennis and Grant and Ross James in rowing. The Bryan brothers have formed one of the most dominant men’s doubles teams and together they earned the Olympic bronze medal in Beijing. The James brothers, meanwhile, will represent Team USA in the men’s eight rowing event.

2.) Siblings: There are six sets of siblings who will be competing for Team USA in London. Diana and Steven Lopez will be competing in taekwondo, and their brother, Jean, who also will be in London, coaches them. The one missing Lopez is Mark, who earned a silver medal in Beijing but did not qualify to compete in London. Diana earned a bronze medal in the 2008 Games; Steven is a two-time gold medalist and earned a bronze medal in Beijing. Sailing also features a set of siblings with Paige and Zach Railey (Zach earned a silver medal in Beijing; Paige won a gold medal in Laser Radial at the Pan American Games.) Water polo’s Jessica and Maggie Steffans and field hockey’s Julia and Katie Reinprecht will be teammates in London. Serena and Venus Williams, who won Olympic tennis gold medals in women’s doubles in 2000 and 2008, are looking to strike gold a third time together at these Games. Haley Anderson qualified to compete in open swimming’s 10K event and her big sister, Alyssa, finished sixth in the 200-meter freestyle at the U.S. Olympic Trials to qualify for the U.S. swimming team’s 4 x 200 relay in London. The sisters also represented the United States together at the 2009 FINA World Championships.